Jumping spiders watch people and videos

Jumping spiders such as this Phidipus audax spider use their seondary eyes to detect motion. The two anterior lateral eyes to detect motion in front, while the posterior lateral eyes detect motion from the side or behind.(Source: Kaldari/Wikimedia Commons)

"I doubt that they mistake large objects, such as people, as prey, but they are certainly interested to know whether you pose a danger."

"If you pull a thread past one, it will often attack it, much like a cat would attack a string. They make good cheap pets!" adds Jakob, a professor in the University of Massachusetts Amherst Department of Psychology and a researcher in the field of organismic and evolutionary biology.

She notes that a lot of misinformation on the web suggests that the bite of these spiders is quite dangerous. She said that the spiders rarely bite humans and, if they do, "not much happens. I got a red spot that quickly went away."

Eight-eye test

For the study, Jakob and colleagues Lauren Spano and Skye Long showed jumping spiders (family Salticidae) videos and conducted other tests to better determine how the arachnids' vision system works. Some spiders have just two eyes, but jumping spiders have four pairs of eyes.

Two principal eyes face forward.

"When you look at a jumping spider, and when it looks back at you, you will notice the very large principal eyes in front," she says. "These have a very unusual structure. They have a large, fixed lens and a tiny boomerang-shaped retina that provides high resolution images and sees in both colour and UV."

The retina in each primary eye sits at the back of a long, moveable tube inside of the spider's head. The spider can move these tubes in order to scan all around, explains Jakob.

"A metaphor another researcher uses that I like is that it is almost as if the spider is looking around with a flashlight," she says.

The other three pairs of eyes are, as a group, called the secondary eyes. They still have excellent vision, and are particularly good at detecting motion. Of these, one pair faces forward and to the side. One pair is very tiny and also faces to a side. The last pair is situated to the side and rear of the spider.

Curious nature

Jumping spiders not only have keen vision, but also a gregarious nature and a seemingly insatiable curiosity about humans and nearly everything else.

"If a spider turns to look at you, it is almost certainly a jumping spider," Jakob says, adding that they respond to their own mirror images and watch videos showing insects.

When shown videos of moving crickets, the spiders will attack the screen. You "can hear the click of their fangs on the screen" as they try to chomp the virtual insects, says Jakob. In the wild, they stalk prey "much like a cat stalks a mouse, following it and tackling it," she adds.

Ximena Nelson, a senior lecturer at the University of Canterbury's School of Biological Sciences, says the conclusions of this new study "are very interesting."

Jakob and her team are now helping to build an eye-tracker to allow them to track the spiders' principal eyes as they explore images. This will allow the scientists to "get a window into the spider's brain in a way that hasn't been possible before."